What creates a huge earthquake? Scientists investigate phenomenon behind big tremors

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Scientists have made further strides toward identifying the key circumstances for catastrophic earthquakes, according to researchers.

What separates a region prone to mild earthquakes compared to those that could see earth-shattering quakes in the future could come down to a principle of friction, according to a new study published last week in the peer-reviewed journal Science.

Friction describes the force of resistance when two materials are sliding against each other. One specific frictional phenomenon that dictates how quickly faults heal after an earthquake may also be key to identifying if they will be at risk of a greater earthquake in the future, according to researchers.

Essentially, faults that heal faster after an earthquake may produce more rigid foundations that are more likely to split dramatically at some point in the future, while faults that heal more slowly allow for more continuous, harmless movement along the fault.

It could allow researchers to begin to zero in on danger zones.

"The same physics and logic should apply to all different kinds of faults around the world," Demian Saffer, director of the University of Texas Institute for Geophysics at the Jackson School of Geosciences and the study's co-lead author, said in a press release. "With the right samples and field observations, we can now start to make testable predictions about how big and how often large seismic slip events might occur on other major faults like Cascadia in the Pacific Northwest."

The reason that earthquakes happen at all is because the earth’s crust is not one solid, unmoving piece. Instead, it’s made up of numerous tectonic plates that move very slowly as the earth’s molten core continues to move. This is the reason that continents have drifted over the earth’s lifespan.

Geological faults are splits in the earth’s crust and the layers of rock above it. There are faults where each tectonic plate meets another, but there are also faults that don’t line up exactly with the plate boundaries. The earth has layers upon layers of rock moving slowly in relation to each other, which occasionally create the right frictional circumstances for an earthquake.

During an earthquake, that regular movement that we can’t detect in our everyday lives is disrupted by sudden movement along the fault. This movement also sends out shockwaves that can be felt by all of those within the radius of the earthquake itself.

Earthquakes can vary wildly in size and strength, with the worst quakes capable of upending buildings, tearing apart cities and ending thousands of lives in an instant.

The magnitude 7.8 earthquake that struck Turkiye and Syria in early February has so far killed nearly 45,000 people, according to recent counts. On Monday, there were reports of even more buildings collapsing in the Hatay province of Turkiye as another 6.4 magnitude earthquake struck the region.

The destructive potential of earthquakes underlines how important it is to try and unravel the mechanisms behind large quakes.

In pursuit of that goal, researchers created a test for this new study that looked at rocks from a well-known fault off of the coast of New Zealand.

This particular fault is prone to “slow motion” earthquakes every so often, and is composed of clay-rich rocks.

Researchers took the rocks, which had been extracted from around half a mile under the seafloor, and squeezed them within a hydraulic press to investigate how quickly they could heal from this pressure, as well as whether they slipped against each other easily or displayed a higher amount of friction. They found the rocks healed slowly, and moved easily against each other.

When put into a computer model, this data predicted that rocks of this type would be associated with a small, slow-motion earthquake around every two years, which aligns almost exactly with the actual data from this fault in New Zealand.

What researchers believe this indicates is that these clay-rich rocks, which are present at many earthquake sites across the globe, actually help slow down and calm earthquakes by facilitating the slow movement of plates against each other. By allowing for more movement within the plates instead of the rocks healing back together quite quickly and resisting movement for a longer period of time, the resulting earthquakes are smaller and more frequent.

It’s the same frictional phenomenon that explains why it takes more effort to move a stationary box at the beginning than it does to keep it moving, researchers say.

So does this mean we’ve got the key to predicting when and where the next big earthquake could be?

Not yet, researchers say—there’s still a lot of work to do before predicting earthquakes becomes that simple. But this research could indicate which faults are capable of huge tremors.

"This doesn't get us any closer to actually predicting earthquakes, but it does tell us whether a fault is likely to slip silently with no earthquakes, or have large ground-shaking earthquakes," Srisharan Shreedharan, assistant professor at Utah State University and study co-lead, said in the release.

We already know that some large faults have no history of the kind of smaller tremors that this study believes are a sign of slow-healing, safer rock structures.

The Cascadia fault, a tectonic plate boundary that stretches down the coast of North America from Vancouver Island down to northern California in the U.S., has no such history, for example.

The Pacific Northwest Seismic Network is hoping to place sensors on key areas of this fault in order to study whether it is hiding the potential for a devastating earthquake in the future. Director Harold Tobin, who was not involved in this new study, said that the study results give them a clear reason to proceed.

"We want to zero in on the processes in the shallow part of the fault because that's what governs the size of the tsunami," Tobin said in the release. "Fault healing doesn't explain everything, but it does give us a window into the working of subduction zone faults that we didn't have before."